1. Field of the Invention
The present invention relates to a chemical-mechanical polishing machine. More particularly, the present invention relates to cleaning system with automatically controlled brush pressure.
2. Description of the Related Art
In the semiconductor process, planarization is an important technique for the treatment of high-density photolithography. A planar surface without irregularities can prevent exposure light from being scattered, so that a fine pattern can be precisely transferred to a wafer. Typically, planarization techniques include spin-on glass (SOG) and chemical-mechanical polishing (CMP). However. SOG cannot supply a sufficient degree of planarity as the wire width approaches to the sub-half-micron level. Therefore, CMP is the only technique that currently can provide global planarization in very large scale integration (VLSI) and ultra large scale integration (ULSI).
CMP is a planarization process that planarizes an uneven surface by applying mechanical polishing and adding a suitable slurry. Generally, slurry is formed by a composition of abrasive particles such as colloidal silica or dispersed alumina and an alkaloid solution such as potassium hydroxide solution or ammonium. The size of these high hardness particles dispersed in the slurry is about 0.1-2.0 .mu.m. Usually before the slurry is driven to the polishing pad of the CMP machine to perform a CMP process, the slurry is filtered through a filter to protect the wafer from being scratched by impurities in the slurry. After the CMP process is performed, the residual slurry is removed completely from the wafer by scouring, spray-cleaning, ultrasonic cleaning, etc.
Conventionally, in the scouring method, the proximity of the brush heads can be adjusted statically to match the surface of the wafer in order to scour both sides of the wafer. However, during scouring, the proximity of the brush heads to the wafer cannot be changed, so there is no dynamic response to a wafer-cleaning process once the process begins. This inability to adjust the brushes gives rise to the formation of microscratches on the water.